Auxiliary control unit

ABSTRACT

The invention relates to an auxiliary unit included in a control arrangement for an internal combustion engine. An NTC-resistor (6) which is subjected to the effect of engine temperature of engine cooling-water temperature, is connected to a control system (5) which monitors the resistance of the NTC-resistor (6), this resistance varying with engine temperature, and utilizes this variation in resistance to change temperature-dependent control parameters for engine operation. The auxiliary control unit is connected to NTC-resistor (6). The auxiliary control unit applies an elevated voltage across the NTC-resistor over a predetermined period of time after an engine cold start, so as to deceive the control system (5) in indicating that the resistor is colder than it actually is.

The present invention relates to a control unit and more particularly toan auxiliary control unit which is connected to a resistor having ahigh-temperature coefficient used to detect the engine temperature orthe temperature of the engine coolant, and which coacts with a controlsystem which functions to adapt the fuel-injection and timing of theengine while driving the engine until the engine is warm.

An engine which is equipped with this type of control systemincorporating an NTC-resistor (negative temperature coefficient) willnormally start easily within a normal operating range of between +5° C.and +20° C. Problems occur, however, when the engine is subjected toload immediately upon being started-up, for instance when the driver ofthe vehicle moves the gear into drive and commences to drive the vehicleimmediately, or when the air condition system is operative or the servopump is working The engine will then tend to die, therewithnecessitating a restart. This is said to be due to a combination offactors relating to engine temperature, poor fuel supply and, in somecases, fuel starvation due, inter alia, to carbon deposits on thesuction valve.

In accordance with the invention, this problem is solved by providing anauxiliary control unit having the characteristic features set forthbelow.

The invention will now be described in more detail with reference to theaccompanying drawings, in which

FIG. 1 illustrates very schematically in block form a control system foran internal combustion engine and shows the location of the inventiveauxiliary control unit;

FIG. 2 is a block schematic of one embodiment of the inventive auxiliarycontrol unit; and

FIG. 3 illustrates the circuitry of one embodiment of the inventiveauxiliary control unit.

Like components have been identified with like reference signs in allthree figures of the drawings.

In the arrangement illustrated in FIG. 1, the positive terminal of abattery 2 is connected to the voltage supply of a conventionalvehicle-engine control system 5, via an ignition lock switch 3 Thecontrol system 5 is operative to control the amount of fuel delivered tothe engine and is connected to an engine temperature sensor or an enginecoolant sensor in the form of a resistor 6 having a high temperaturecoefficient. The resistor used will normally have a negative temperaturecoefficient, known as an NTC-resistor, although the use of a resistorwhich has a positive temperature coefficient is not excluded. The outputsignals of the control system are functions, inter alia, of thetemperature detected by the resistor 6.

In accordance with the invention, an auxiliary control unit 7 is alsoconnected to the resistor 6. Voltage is supplied to the auxiliarycontrol unit 7 in the same manner as that in which voltage is suppliedto the control system 5, and the auxiliary control unit 7 has an inputTRIGG, which in the case of the illustrated embodiment is connected tothe oil-pressure monitor-switch 4 of the engine, this monitor-switchbeing connected to the positive terminal of the battery via anoil-pressure lamp 8 and the aforesaidignition lock 3. When theoil-pressure monitor-switch is broken, the oil-pressure lamp 8 isextinguished and the potential on the input TRIGG will therefore behigh, therewith triggering the inventive auxiliary control unit.

The significant factor with the signal TRIGG is that the engine willhave started before the auxiliary control unit is triggered. This isnecessary in order to prevent an erroneous NTC-voltage from deceivingthe λ-probe integrator, i.e. when a temperature beneath about 14° C. isregistered at the very moment of starting the engine, the probe-start isdelayed, resulting in emission problems. Generator voltage, engine speedetc. may also constitute trigger parameters which can be used in thepresent context, i.e. other than oil-pressure.

In accordance with the present invention, on the occurrence of a coldengine-start, where the temperature of the engine is, for instance,between +5° C. and +30° C., the voltage across the resistor 6 is changedto a value which indicates to the control system 5 that the resistor 6is colder than it actually is, and the control system causes the outputsignals thereof to change accordingly. Thus, when the resistor 6 is anNTC-resistor, the voltage shall be raised. The control system 5 ofseveral models of vehicle has separate control functions which becomeoperative when the engine 1 has a lower temperature than about +5° C.These separate control functions must not be interferred separatecontrol functions must not be interferred with. When the engine 1 has atemperature higher than about +30° C., the engine is sufficiently hot toobviate the need of the additional function afforded by the auxiliarycontrol unit 7.

This additional function corresponds to the function of an additionalchoke and will therefore only remain operative for a predeterminedlength of time subsequent to starting the engine. This time period maybe in the order of 60 seconds and is not commenced until the oilpressure has reached its set-point value, i.e. when the voltage TRIGG ishigh and the lamp 8 is extinguished.

The elevated voltage across the resistor 6 during said predeterminedtime period may, for instance, be essentially the same over the whole ofthe temperature range +5° to +30° C., which enables the circuit requiredto be given a simple construction, or alternatively the voltage increasemay be essentially constant, i.e. different elevated voltages may occurover said temperature range. For instance, when the engine temperatureis +15° C. and the voltage across the NTC-resistor is increased by 0.5V, the control system 5 will function as though the engine temperaturewere about 10° C. lower than it actually is.

FIG. 2 illustrates schematically an embodiment of a circuit which willprovide an essentially constant increased voltage during the period inwhich it is active. The circuit is a series-coupling consisting of theNTC-resistor 6 and a resistor R connected between the positive-conductorA and earth. When the ignition lock switch 3 is made, the voltage Sacross the NTC-resistor 6 is sensed by a sensor 9. When the voltage Slies within a range which indicates a resistance of the NTC-resistorcorresponding to the temperature range of +5±0.1° C. and +30±0.1° C.,the sensor 9 produces an output signal, which is sent to a lockingcircuit 10. The circuit 10 normally has a low output signal. Whenreceiving the signal from the sensor 9, the output signal of the lockingcircuit is switched to a high value. The output signal of the lockingcircuit is thereafter locked in this state. A diode 11 is connectedbetween the output of the locking circuit 10 and the NTC-resistor, andis so directed that the voltage on the output of the locking circuitwill only influence the voltage across the NTC-resistor 6 when saidvoltage is high. A time circuit 12 is connected between the output ofthe locking circuit 10 and earth. This time circuit is normallynon-conductive and is triggered when the oil-pressure voltage becomeshigh. When a set time period has lapsed after the trigger signal, e.g.60 seconds, the time circuit is switched to a conductive state, suchthat the output signal of the locking circuit will obtain a low voltagelevel via the time circuit, and thereafter retain its conductive stateuntil the supply of voltage to the auxiliary control unit 7 is switchedoff or until the oil-pressure voltage becomes low.

The auxiliary control unit 9-12 according to the invention is constantlyconnected to the NTC-resistor. The time circuit 12 is startedautomatically when triggering takes place, irrespective of the state ofthe locking-circuit output. Consequently, when a start takes place at atemperature which is lower than about +5° C. and the engine temperaturelies within the range of +5° C. to +30° C. within the 60 second timeperiod set on the time circuit, the inventive auxiliary control unitwill be activated during the remainder of this set time-period.

FIG. 3 illustrates an embodiment of a circuit according to FIG. 2. TheNTC-resistor is connected to the conductor A via the series-resistors R1and R2, and the conductor A is connected to the positive terminal of thebattery (not shown in FIG. 3) via the ignition lock switch 3. Thejunction between the resistors R1 and R2 is connected to the (-)-inputof a first comparator IC1 and to the (+)-input of a second comparatorIC2. All of the comparators included in the circuit have voltage supplybetween earth and the conductor A, although this is not shownseparately.

A series-coupling comprising a zener diode DZ1 and a resistor R3 isconnected between earth and the conductor A. A voltage divider havingresistances R4 and R5 is connected across the zener diode DZ1 and theoutput of the voltage divider is connected to the (+)-input of thecomparator IC1. The voltage divider is dimensioned so that thecomparator IC1 will produce a high signal when the resistance of theNTC-resistor corresponds to a temperature higher than +5±0.1° C. Thistolerance factor of 0.1° C. is mainly due to the fact that theNTC-resistor used in this context is permitted to have a relatively widetolerance range.

A voltage divider with resistors R6 and R7 is also connected across thezener diode DZl. Its output is connected to the (-)-input of thecomparator IC2. The resistors R6 and R7 are dimensioned so that theoutput of the comparator IC2 will only be high when the NTC-resistor issubjected to a temperature beneath +30° C.±0.1° C.

The outputs of the comparators IC1 and IC2 are connected together viarespective resistors R8 and R9. The junction P is connected to the(+)-input of a third comparator IC3. The point P is also connected toearth, via a resistor R10, and also to the oil-pressure monitor-switch,via a diode D1. Consequently, the junction P is always connected toearth via the oil-pressure monitor-switch, prior to the engineoil-pressure rising to its set-point value.

The (-)-input of the comparator IC3 is connected to the output of avoltage divider R11 and R12 which is connected between earth and theconductor A. This dimensioning is not particularly critical, since thefunction of the comparator IC3 is merely to distinguish between a highor low potential at the junction P, i.e. to discern when the outputs ofboth comparators IC1 and IC2 are high and the oil monitor-switch isactivated, or when any one of these signals deviates.

As soon as the junction P has a high level, the comparator IC3 switchesits output from a low to a high level. A series-coupling comprising adiode D2 and a resistor R13 connected between the output and the(+)-input of the comparator locks the comparator output at a high levelonce having been switched. Thus, the comparator IC3 cannot be switchedagain to a low output signal before voltage supply to the auxiliarycontrol unit is interrupted. The output of the comparator IC3 isconnected to the NTC-resistor via a resistor R14 and twoseries-connected diodes D3 and D4, and is operative to raise the voltageacross the NTC-resistor when its output has a high voltage level. Theoutput of the comparator IC3 can, in this instance, be considered toform a constant voltage source and the resistor R14 and the NTC-resistorcan be considered to form a voltage divider. The relationships betweenthe resistances of R14 and the NTC-resistor can be selected so as toobtain essentially the desired nature of voltage increase across theNTC-resistor.

In the case of the illustrated embodiment, the time circuit includes afourth comparator IC4, the (+)-input of which is connected to the outputof a voltage divider R15 and R16 which in turn is connected betweenearth and the conductor A.

This output has a relatively high voltage level. The (-)-output of thefourth comparator IC4 is connected to the output of a series-couplingcomprising a capacitor C of high capacitance and a resistor R17connected between earth and the input "TRIGG". When the input "TRIGG"goes high, the capacitor C is slowly charged. The capacitor C and theresistor R17 are dimensioned so that the potential on the (-)-input ofthe fourth comparator IC4 reaches the potential on its (+)-input afterabout 60 seconds. At the end of this time period, the comparator IC4switches its output from a high level to a low level. The output of thecomparator IC3 is then connected to this low voltage level, via theresistor R14 and a diode D5 located between the resistor R14 and theoutput of the fourth comparator IC4. The potential on the junctionbetween the resistor R14 and the diode D3 will then be low. The elevatedvoltage across the NTC-resistor then ceases.

A safety circuit which functions to protect the comparator IC4 againstback current caused by transients includes a series-coupling comprisinga diode D6 and a resistor R18 connected across the resistor R17. A diodeD7 is connected between the junction between the diode D6 and theresistor R18 and the conductor A.

It will be understood that many modifications can be made within thescope of the invention. For instance, the time circuit may have aconfiguration different to that illustrated in FIG. 3. Instead ofconnecting a capacitor C so that said capacitor will be charged to adisconnect-potential subsequent to receiving a triggering signal, thecapacitor can be connected so as to be charged quickly and immediatelyvoltage is applied to the circuit and then caused to discharge slowlyupon receipt of a triggering signal. The capacitor included in the timecircuit may also be connected to the (+)-conductor A instead of beingconnected to earth.

I claim:
 1. An auxiliary control unit included in a control arrangementfor an internal combustion engine in which a resistor (6) subjected toengine temperature or cooling-water temperature is connected to acontrol system (5) which monitors the variation of the resistance of theresistor (6) with engine temperature and utilizes this resistancevariation for changing temperature-dependent control parameters forengine operation, characterized in that the auxiliary control unit isconnected to the resistor (6) and, over a predetermined time intervalafter an engine cold-start, is operative to set a changed voltage acrossthe resistor to a value which indicates to the control system (5) thatthe resistor (6) is colder than it actually is.
 2. An auxiliary unitaccording to claim 1, where the resistor is an NTC-resistor,characterized in that the auxiliary control unit is operative to applyan elevated voltage across the resistor during said predetermined timeperiod.
 3. An auxiliary unit according to claim 1, characterized in thatthe predetermined time period is initiated by an external signal (TRIGG)which is produced subsequent to an engine start.
 4. An auxiliary unitaccording to claim 1, characterized in that the auxiliary control unitis intended to come into operation solely when the voltage across theresistor, as detected prior to its coming into operation, indicates thatthe temperature of the resistor exceeds a predetermined lowesttemperature, e.g. +5° C.
 5. An auxiliary unit according to claim 1,characterized in that the auxiliary control unit is intended to comeinto operation solely when the voltage across the resistor, as detectedbefore coming into operation, indicates that the temperature of theresistor is beneath a predetermined highest temperature, for instance+30° C.
 6. An auxiliary unit according to claim 1, characterized in thatthe changed voltage is an approximately constant voltage-change inrelation to the voltage normally prevailing across the resistor.
 7. Anauxiliary unit according to claim 1, characterized in that the changedvoltage is approximately constant and is independent of the voltagewhich normally prevails across the resistor.
 8. An auxiliary unitaccording to claim 7, characterized by a detecting circuit (9; IC1, IC2)connected to the resistor (6; NTC) such as to detect, on the basis ofthe resistance of said resistor, whether its temperature lies within atemperature range in which the auxiliary control unit shall be broughtinto operation, and if such is the case to produce an output signal on alocking circuit (10; IC3, D2, R13) connected to the output of thedetecting circuit, such as to lock said circuit in a state which givesthe changed voltage across the resistor subsequent to receipt of asignal from the detecting circuit, the output of the locking circuitbeing connected to the resistor (6; NTC), and by a time circuit (12;IC4, C, R17) connected to the output of the locking circuit, said timecircuit functioning to interrupt the effect of the locking-circuitoutput on the resistor subsequent to the lapse of a predetermined timeperiod after triggering of said locking circuit.
 9. An auxiliary unitaccording to claim 8, characterized in that the trigger-input of thetime circuit is connected to a unit which produces a signal after theengine has been started, for instance, the oil-pressure monitor-switchof the engine.